BAGHDAD, Oct. 24 -- The top American commander in Iraq said Tuesday that he may call for more troops to be sent to Baghdad, possibly by increasing the overall U.S. presence in Iraq, as rising bloodshed pushes Iraqi and American deaths to some of their highest levels of the war.

The commander, Gen. George W. Casey Jr., also said he now believed Iraqi forces would be ready to take over security responsibility from the Americans no sooner than late 2007 or early 2008. The announcement of a 12- to 18-month target again pushes back the withdrawal of the bulk of the 145,000 or so U.S. troops in Iraq.

Casey spoke alongside U.S. Ambassador Zalmay Khalilzad at a rare joint news conference in Baghdad's Green Zone, aiming to show that U.S. and Iraqi leaders were confronting surging sectarian violence. Both men acknowledged that both the course and nature of the war have changed this year, as Iraq's Shiite Muslim majority and Sunni minority battle for power, resources and, lately, survival.

"Make no mistake about it: We are in a tough fight here in the center of the country and in Anbar province," Casey said, emphasizing that the worst of the bloodletting was in Baghdad.

"This is not a country that is awash in sectarian violence," Casey said. "The situation's hard, but it's not a country that's awash in sectarian violence."

Casey said later that any additional troops for Baghdad could come from a variety of sources, including from the Iraqi military, from U.S. forces elsewhere in Iraq or from outside the theater.

Khalilzad framed the Iraqi conflict as part of the struggle for security in the Middle East, which he called "the challenge of our age." He sought to rally flagging public support in the United States for the war and answer calls -- led by Democrats -- to set a timeline for American withdrawal.

"The recent sectarian bloodshed in Iraq causes many to question whether the United States and the Iraqis can succeed," Khalilzad said. "My message today is straightforward: Despite the difficult challenges we face, success in Iraq is possible and can be achieved on a realistic timetable."

But events inside and outside the Green Zone on Tuesday highlighted the stubbornness of the basic problems with which U.S. forces have struggled since the 2003 invasion: security and infrastructure. Killings by insurgents in the western province of Anbar helped push up the October death toll among American troops in Iraq by four service members to 91, the U.S. military said Tuesday, the highest monthly total for American forces in the country in 12 months.

And Casey and Khalilzad, the top U.S. military and civilian leaders in Iraq, were left for several minutes to deliver their remarks in darkness illuminated only by the battery-powered lights of TV camera crews. One of Baghdad's frequent power outages cut electricity to the converted parking garage that houses the U.S. military press center, briefly knocking the internationally broadcast conference off the air.

For Casey and his predecessors, the question of whether President Bush dedicated enough troops to the Iraq war has been one of those most frequently asked -- and hotly debated. While Casey has raised troop strength temporarily as high as 150,000 for Iraqi national elections, his stock answer has been that if he felt additional troops were needed, he would ask for them.

On Tuesday, Casey said he might ask for them. If Iraqi leaders can resolve their differences and if Iraqi security forces improve, "I think [we] can put Iraq in a very good place in 12 months.

"Now, do we need more troops to do that? Maybe."

It is not clear whether Iraqi or U.S. forces in Iraq, which already are stretched thin, could provide substantially more troops for duty in the capital, however.

American commanders have complained, usually privately, that the Iraqi government has failed to provide many of the Iraqi troops they requested earlier to try to stabilize Baghdad. In September, commanders had a weeks-old request for 3,000 more Iraqi troops for the capital; only a few hundred arrived, Maj. Gen. James D. Thurman, the U.S. commander for Baghdad, said last month. Some Iraqi battalions have mutinied rather than answer orders to deploy to Baghdad.

U.S. commanders moved at least 6,000 more American troops to Baghdad over the summer for Operation Together Forward, an effort to arrest the violence in the capital. To get those extra troops, commanders had to take the unpopular step of extending one unit's deployment just as it was going home to its base in Alaska, as well as calling in emergency reserves based in Kuwait.

In all, about 15,000 American troops and 9,000 Iraqi soldiers are now deployed in Baghdad for the special security operation.

Despite the concentration of efforts in the capital, violence here has climbed more than 43 percent since midsummer. Maj. Gen. William B. Caldwell, the top U.S. spokesman in Iraq, said last week that attacks had climbed 22 percent in the first two weeks of the Islamic holy month of Ramadan, which began in late September, compared with the preceding two weeks.

The toll is highest among Iraqi civilians. More than 2,660 Iraqis were killed in Baghdad last month alone, the highest such figure for the war. The average daily number of attacks on Iraqi security forces is also at a high, the U.S. Defense Department said in a report in late August.

Casey said U.S. and Iraqi authorities would adjust their Baghdad military plan to combat the rising attacks. He declined to give specifics.

Iraqis and Americans here face "a difficult situation, and it's likely to remain that way over the near term," Khalilzad said.

U.S. and Iraqi leaders were adjusting political goals in Iraq as well, Khalilzad said, to cope with a conflict that has expanded from an insurgency alone to an insurgency increasingly overshadowed by sectarian violence.

Khalilzad said Iraqi Prime Minister Nouri al-Maliki had agreed to timelines for accomplishing several specific goals, including developing a plan to deal with militias and reforming Iraq's Interior Ministry by the end of the year.

Militias connected to the Shiite religious parties that lead Iraq's government are accused by U.S. officials, Iraqi Sunnis and others of being lead players in increasingly brazen attacks on Sunnis. In the south, where Sunnis are few, Shiite militias fight each other.

According to Khalilzad, Maliki told U.S. officials that Moqtada al-Sadr, the Shiite cleric who leads the most feared militia, had agreed to the creation of a plan for disarming militias.

However, Sadr has said he does not consider his armed followers to be a militia, and thus sees them as outside any plan to break up the militias, according to one diplomat here. It was not clear if Sadr's alleged commitment to Maliki superseded that.

On Tuesday, Sadr called for an end to religious killings.

"I totally reject any Shiite-Shiite fighting or Sunni-Shiite sectarian fighting in Iraq under any pretext," he said in a speech in the southern holy city of Najaf. "Protecting Iraq is our main goal, and the expulsion of the occupation troops from the country is our objective, too."

Armed bands claiming to be part of Sadr's militia have kept up the violence despite similar calls from Sadr in recent months. At least in part, Sadr appears not fully in command of the thousands of armed men claiming allegiance to him.

Iraq's Interior Ministry also is controlled by the Shiite religious parties, and U.S. commanders concede it is heavily infiltrated by the Shiite militias.

Khalilzad said Iraqi leaders have agreed that, over the next 12 months, they will come up with a national compact for reconciliation and a plan that fairly shares Iraq's oil wealth, have a program on militias in place and work on Iraq's security institutions.

Since taking office in May, Maliki has postponed promised action on militias and on national reconciliation, frustrating American officials as the U.S. toll rises and Iraq's divisions deepen. Khalilzad on Tuesday urged Iraqi leaders to "step up" to their responsibilities.

American commanders also have repeatedly set rough dates for when U.S. troops might start to withdraw, only to roll back those dates as Iraq's troubles worsened.

Casey said last year that he hoped for "fairly significant" withdrawals by spring 2006, but he said Tuesday that rising sectarian violence had made such a drawdown impossible.

In Washington, some Democrats responded to Khalilzad's and Casey's messages by demanding that the United States pull out troops if Iraqis miss their deadlines.

"We need to make clear that American troops will be leaving within a year to force Iraqis to make the tough compromises," Sen. John F. Kerry (Mass.) said in a statement. "Only then do we have a chance to make Iraqis stand up for Iraq and bring our troops home."

"We must accelerate the timeline of training Iraqi security forces" and double the number of U.S. trainers, said Rep. Ike Skelton (Mo.), ranking member of the House Armed Services Committee. "American force readiness is at critically low levels and will only fully recover when significant numbers of personnel and equipment can begin to redeploy from Iraq."